1. You'd only see 16 GB of ram operating in single channel mode.2. The 2nd stick would run at 1800 (assuming the mobo supports that 2nd stick)3. The mobo would fail to boot until you change the voltage of the stick and timings to match an 1800 stick.

These are all blind luck guesses as I still only have 4GB of DDR2 and am not tech savvy... so more for the amusement of the rest of you smarties.

I don't think you can answer #1 fully without knowing more about the processor. Doesn't the memory controller dictate whether or not it can read those super-high densities? Or is it part of the BIOS? For instance, my work machine is a Sandy Bridge based Dell Latitude. Officially it supports 8GB of RAM, but there are lots of examples online of people putting 8GB SO-DIMMs in it for a total of 16GB.

So just because the kid's homework says the system "supports" 16GB doesn't mean that it only sees only 16GB no matter what. It could very well not boot, on the other extreme, if the memory density is too high. That was true of some G4-equipped Macs (so the memory controller was part of the chipset, not the CPU) that could not handle PC-100 DIMMs larger than 256MB, and those had to be double-sided DIMMs because the higher density chips weren't compatible. Sawtooth and Gigabit Ethernet G4 towers, IIRC.

I do not understand what I do. For what I want to do, I do not do. But what I hate, I do.

Sheesh, how friendly we are around here. I don't see anything to get worked up about; doesn't smell like spam either. I'll play.

1) Does that not depend on the maximum module size? Most recent motherboards have an 8 GB max module size, if I remember correctly. In the case that you're plugging in higher capacity modules than the mobo can recognize, I'd guess you're mobo won't see any memory at all.

Some motherboards are limited by the chipset. I recall some... Conroe-based Macbooks? that had a hard limit of 3 GB based on the Intel chipset used. Then there's the wonderful bang-for-buck Dell Inspiron 410. It officially supported 4 GB but after a BIOS update it started to support up to 8 GB. But wait, there's more! Most OEMs come with Windows Home Premium (let's go with Win7 for this example) which supports only 16 GB:

So from a practical standpoint, even if your motherboard supported 64 GB of RAM, if you're rocking Win7 Home Premium, you'll only get use of 16 GB of that.

This is a question I myself am curious about, too, as I have a Dell XPS 8300 and the max supported RAM is supposedly 16 GB. I'm probably just going to buy 32 GB of RAM just to see what happens sometime as no one else seems to have done this. Is it limited in the chipset? In the BIOS? By Dell assuming a lowest common denominator of Home Premium and not wanting to be sued for claiming more RAM than it lets the customer see? Who knows!